MTFCA Forum

Has anyone else experienced a kevlar band on the brake drum swelling?

Mine did during a short 10-mile trip and caused the car to stall. Not much room left to loosen the band - running out of threads on the pedal shaft.

I would assume that bands settle in and compress some over time.

Hi Gerald,
NO I find Kevlar needs to be adjusted often until it seats in, then it seems to be great after that and needing very little adjustment.
You just install the Kevlar bands? Could rivets have come loose and let the band material stack up? Do you have auxiliary brakes
that are keeping the peddle from returning? Park brake adjustment interfering with peddle through the equalizer?
I would suggest you find out as to tight Kevlar will cause heat and discontent and engine removal to replace cracked drums.
Craig.

The correct way to install the lining on the bands is to install the two end rivets first and then push the material toward the middle installing the other rivets as you go along. The material must be tight against the metal bend. If not done correctly it will be away from the metal between rivets and will drag on the drum. This is true concerning all the cloth bands and the cloth or scandinavian will wear out fast, but Kevlar will not wear out. It will overheat the drums causing them to turn blue and then crack. So be sure the material is correctly installed.
Norm

I think it's far more likely that the drum is expanding from heat than that the Kevlar is expanding from any cause.

An initial adjustment that is too tight is a common issue with Kevlar.


If loosening the adjustment after everthing has cooled off for several hours does not solve the dragging and allow the pedal to go to within 2" of the floorboard, I'd look for problems with the lining installation, band or spring condition, or the drum or pedal mechanism condition.

The brake pedal should have plenty of free play before the band touches the drum.

Gerald- be sure to get to the bottom of this issue because OE Ford drums were not designed to be used with something unforgiving like kevlar. You could end up with damaged or destroyed drums....


Did you install the linings as Norman mentioned above?

That lump in the band material must sit flat when installed. No high spots to make friction.
Did you have the HH off or install thru the inspection cover? (Huge no no IMO)
I have not experienced a growing/tightening of the band.

Since you stopped driving the car have you put the handbrake in neutral and tried to turn the engine over by hand? If the band is really tight you shouldn’t be able to. Remove the inspection cover and check to see if somthing isn’t letting the band expand. You did mention there isn’t anymore threads on the pedal shaft to do it.
Seems if the car was OK and then stalled after a few miles maybe a rivet or two wasn’t seated correctly and let the band material bunch up and cause a hump inside the band.

If you remove the band and find it’s a band installation issue I would remove all the bands and carefully redo them all. My opinion ———.

A tight brake band would make the car struggle and eventually stop on the road, but it wouldn't make the engine stall.

Check low band and reverse for pedal travel, too. If the engine is too hard to crank, they are more likely the problem.

Dan Haynes wrote: ↑

Fri Jan 13, 2023 9:58 am

A tight brake band would make the car struggle and eventually stop on the road, but it wouldn't make the engine stall.

Really ? I'm laboring under the misconception (?) that the engine is in direct drive in high gear unless the clutch is slipped into "neutral".

Were the bands, or any of them, re-lined or re-installed just prior to the problem arising?

Does the car have any kind of auxillary brakes installed?

Will the engine run normally with the car stopped and the transmission in "neutral"?

Can you push the car on level ground with the transmission in "neutral?

Can you hand crank the engine with the car in "neutral?

A very common problem with the low pedal is a worn cam and notch. In that case, the only way to get the low to work is to tighten the band so much that it drags in neutral and high. That leads to the "big bang" when the drum shatters and locks up the car causing much damage even possible broken crankshaft When you move any of the pedals, they should move to the side as the pedal is depressed. With the brake and reverse the movement is outward and starts soon after beginning to push the pedal. On the low, the pedal moves inward after it is halfway down and continues to compress the band as the pedal is depressed. On right hand drive cars the pedals move opposite direction.
Norm

Rich P. Bingham wrote: ↑

Fri Jan 13, 2023 10:07 am

Dan Haynes wrote: ↑

Fri Jan 13, 2023 9:58 am

A tight brake band would make the car struggle and eventually stop on the road, but it wouldn't make the engine stall.

Really ? I'm laboring under the misconception (?) that the engine is in direct drive in high gear unless the clutch is slipped into "neutral".

If the brake was engaging, the engine can slow & stall like a motor seizing unless the operator gets it in neutral. During hand cranking the brake drum is stationary unless starting in gear with a wheel up. (hint)

The brake drum is the least likely of the 3 drums to crack from over heating, but it can happen. You will want to lift a wheel in gear & have someone slowly turn the motor over, looking @ the drum surface for a crack.

There is little room for error in the mounting, reshaping, installation, adjustment & re-adjustment of kevlar bands. They are unforgiving, not for everyone.

I hope you can easily resolve this issue.

The Kevlar isn't really expanding. The transmission drum may be however, due to excessive heat. Also, when Kevlar gets really hot, it also gets "sticky".

Bottom line, your band was adjusted too tight and the band/drum overheated. Very hard on drums! When you lined the bands, did you do it as described in the posts above?

I'd look for worn cams and too tight settings as others have stated.

"The Kevlar isn't really expanding. The transmission drum may be however, due to excessive heat." The expansion of an 8" diameter cast iron/cast steel 'drum' amounts to + 0.024" when the drum temperature increases from 70F to 500F. True, the part does expand but other variables are more significant in causing the observed problems. jb

It is normal for the brake drum to expand by whatever amount when it is in use. It's not an issue unless the band is too tight to begin with. Apparently this issue, whatever it proves to be, developed over the course of a ten mile drive. What is the melting point of Kevlar, assuming it has one? It must be high, since Kevlar is used for heavy duty clutch linings.

TXGOAT2 wrote: ↑

Fri Jan 13, 2023 1:48 pm

It is normal for the brake drum to expand by whatever amount when it is in use. It's not an issue unless the band is too tight to begin with. Apparently this issue, whatever it proves to be, developed over the course of a ten mile drive. What is the melting point of Kevlar, assuming it has one? It must be high, since Kevlar is used for heavy duty clutch linings.

From our good friends who run the internet...

"Unlike most plastics it does not melt: it's reasonably good at withstanding temperatures and decomposes only at about 450°C (850°F). Unlike its sister material, Nomex, Kevlar can be ignited but burning usually stops when the heat source is removed."

Rich P. Bingham wrote: ↑

Fri Jan 13, 2023 10:07 am

Dan Haynes wrote: ↑

Fri Jan 13, 2023 9:58 am

A tight brake band would make the car struggle and eventually stop on the road, but it wouldn't make the engine stall.

Really ? I'm laboring under the misconception (?) that the engine is in direct drive in high gear unless the clutch is slipped into "neutral".

Well, yeah, Rich. If the car began to labor and lose speed to the point it was bucking and jerking, I would release the clutch and - maybe wrongly - assumed anybody would.

I would focus on the 3 clutch fingers first...if only to eliminate the idea

Based on personal experience....

I had rebuilt a car, the area had small hills but nothing dramatic and the car started and ran around the neighborhood fine. Drove it to the first Elgin Road race-enactment, it did well, went to take it home and get ready for the banquet and on the one hill involved in getting back to my house...it started behaving exactly as you describe! (except it had Scandia linings). Long cute story about how it got home, but I was obviously disgusted with it, couldn't get it to now behave even in the neighborhood, and then after a while I deduced that all I had done should have been good and for reasons unknown..I pulled the inspection cover, pulled the clutch finger cotters, and backed off one turn on all three and reseated the cotters!

Buttoned it up,,,,,,then ran fine and to this day now decades later still has those exact finger settings and won't crawl across the floor when cranked Go figure...sometimes known setting numbers (such as spring length) are in fact just starting points??? (especially when heat growth is involved?)

Norm, the pedal action for both RHD & LHD are the same.
Reverse and brake pedal shaft move to the left
The low pedal moves to the right.
This drawing shows the action
The black vertical line is the HH
On LHD the cams are on the outside for Reverse and Brake the Low cam is inside
On RHD the R & B is on the inside and the Low is outside.
Pushing the pedals results in the same sideways movement and clamping action of the drums.